Corals belong to the animal phylum Cnidaria that also includes jellyfish and sea anemones. Coral polyps generally have a brown coloration that is the result of single-celled algae that live inside the cells of the coral animal. The algal cells are protected and relatively safe inside the coral polyps. The algal cells also get plenty of light and lots of carbon dioxide inside the host cell, allowing them to undergo a lot of photosynthesis. Some of the food produced by the algal cells is transferred to the coral host cell, giving them nutrients. This type of interaction between algae and coral would be considered ...